Monobasic salts of phosphate acids as stabilizers for diazotype prints



Patented Nov. 29, 1949 UNITED STATES-- 2,489,728 M 'NQB .S L D iiQSIHKTE 1 1 .38" AS STABILIZERS'IFOR DIAZOTYPE PRINTS sum 0. Slifki n; BifigTiamton Nl Y.',- assignof to I General Anilir'ie"& Film Corporation; New York; N. Y., a eorpora-t'iomof Delaware No Drawing; Application September 1 6 1 9 47 Serial No. 774',4 38- This inventionr'elates to an'improvem fitinthe production of photographic prints 'b'ytli' diaz'o typeproee'ss. I

In the preparation of diazotyp' prints asordi narilycarriedout, a carrier surface or base'lSe'aring a light-sensitive diazo compound rsexposeu to light of locally varied intensity (e. g. under a photographic transparency or an opaque design or line drawing on a transparent sheet) so as to destroy the diazo compound partly or completely in the illuminated ar'eas. Indeveloping the print; the residual diazo'compound corre's'ponding tot image to be reproduced 'is coupled with arr" a'zo" coupling component, which may be originallyin: corporated with the dime compound on the car rier, or subsequentlyapplied theretoiria d'eveloper composition. When the azo couplingfcomponent is originally present together" with the light-sensitive diazo compound" on the" photoprinting material; development cambe'advant geou's'ly efiected by the dry process '(i'i'e. bye posure' to an alkaline vapor such: asammonia). Such prints can also" be developed by a semi wet process wherein the exposed print'ifi'moistene'tf with small amounts of a solution adapted to effeet coupling (e. g. a solution of alkaline reacting substance), such solution being allowed to dry on the resulting print. When no coupling component' is included'in the photopifinting' material; it may be-applied together withthe alkaline reagent" which promotes coupling in the solution "em-"'- ployed in the semi-wet developing p'rocessr I In the aforesaid dry and semi-wet developing processes, the excess coupling component-and also" decomposition products of the light sensitive' diazo compound, remain on the surface; of'the finished print, particularly in the background areas. These materials causeseriousdiscoloraf tion' of the background on exposure of the print to light and/or air, whereby the appearance and '4 clarity of the copy is seriously impaired. Numei ous attempts have been made to" improve the aging qualities of such prints, for example by incorporating stabilizers in the sensitizing or developing composition, but such proposals are generally only partly efiective.

It has also been proposed to remove-the injurious byproducts and excess couplingcomponenpm by" washing the developed print with water; Considerable improvement is effected thereby insofar as-the stability ofthe background to discol-' oration is concerned, but such treatment often 1 causes undesirable color changes in-thedeveloped image. For example,- black dyed prints Whenwashed with water have a marked tendency to b wherein arange of 'shadows of varying' depth butr 2- of the-samecolor (particul'arly blaclr) is to be pro-" du'cedr I- have diseovered-'-thatdiaZotype prints:proidu'ced -by the dr'y-or semi-'wet development prod-'- esses andtherefore: carrying substantial amounts of coupler and diazo compound decompositionw products on the surface oi the print, can be effectively stabilized against 'disiicilr'ifation on exposure to light and/or air without causing undesirable thangesin the 061"" of theimage} by washing the pri'fi'ts 'withan aqueous solution of a water-$5111 bl iiiorio b'asic aw of a" phosphate acid, particularly' a mono-alkali metal or ammonium salt" of rrosphtricaeid-or of lower alkyl mono: or" diesters of phosphoric-acid the; solution having 5 PH of at least'5 andless than 7.

Phosphoric acids employed at. cordanee'withmy inven on may be represented by"thefollowin'g"general formula"? corisi'sting' of (i.e-alkyl= g-rou-p is se'le'cite'dno" the? group consis metals and the ammonium" The aforesaid-seem; fpr'e'srited by thephov' formula; are advantageously: employedinf an aqueous sohil'liori 'in ga coheentraubnor atlea 1% 'an'd preferably 6F'about--5%c Wherrthe col compound-of the ima e is relatively soluble in w te1-,'-'a-r1y tendency of e color to run during th washing treatment-can overcome by including a neutral salt (629. NtiCBGr Na'zSOr) ifr-the wa sh ing s'olution for exampl in a concentration o'f about"5% .3

'thewashingr treatment is coirip1ete; -the print-1s allowed to d rs i The resmtihg:co ies'are sub'sta'n'tially =imrtiu-rle to discoloration upon e posur'e' to light: aridlo air;-andthe* co1oi ofthe print as originallydeveloped is preserved witho' change, even when the seiis'iti'z'ed' base materialis adayer'of gelatin" Y H Myiinventiomis illustratedby 'the following ex amplesw ting or 'allalr- Example 1 tized in the usual manner by impregnation with sensitizing compositions containing the following combinations of diazo compound and coupler:

A. 2-diazo-l-naphtholl-sulfonic acid and phloroglucinol B. p-Diazo-diphenylamine sulfate and 2-naphthol-3,6-disodium sulfonate C. Zinc chloride double salt of p-diazo dimethylaniline and 2,3-dihydroxynaphthalene The developed prints were washed in accordance with my invention with'a 5% aqueous solution of sodium dihydrogen phosphate and thereupon dried. The resulting washed copies showed no yellowing or discoloration'on exposure to light and air for prolonged periods, and the'color of the print as originally developed remained unchanged.

Example 2 A series of prints prepared and developed in the same manner as in Example 1 and having strongly-contrasting image and background discoloration of a diazotype print, bearing residual unreacted coupling component and diazo compound decomposition products on the background areas thereof, which comprises the step of washing said print after its development with an aqueous solution of a compound having the general formula:

, wherein R1 and R2 are selected from the group wherein R1 and R2 are selected from the group consisting of hydrogen and alkyl groups of 1 to 3 carbon atoms, and M is selected from the group areas, were washed with an aqueous solution,

containing 5% sodium dihydrogen phosphate and 5% sodium chloride and thereupon dried. The. copies thus obtained possessed stability against.

discoloration similar to that obtained in the foregoing example, and the edges of the image portion were perfectly defined, showing no tendency of the color to run.

Example 3' A third set of prints prepared and developed as in Example 1 were washed with a 5% aqueous solution of sodium or potassium monoethyl hydro j gen phosphate, and thereupon dried. The copies thus obtained likewise possessed excellent stability to discoloration as was the case with the prints of the preceding examples.

Instead of the sodium or potassium salts employed in the foregoing examples, the corresponding ammonium salts can be used. Similarly, other mono-alkali metal salts of lower alkyl (i. e. methyl, ethyl, propyl or isopropyl) monoor di-esters of phosphoric acid can be used instead of the sodium or potassium ethyl hydrogenphosphate in Example 3. The pH of the washing solution in-each of the foregoing examples is between 5 and 7. If necessary, small amounts of buffers, acids or alkalies can be added to adjust the pH of the solution to the aforesaid range. For example, small amounts of acid may be advantageously used in connection with mono alkali metal dialkyl phosphates. The washing treatment of my invention can be applied with a similarly advantageous effect to diazotype prints having other kinds of bases or carriers (e. g. ordinary paper, cellulosic films or the like). I

Iclaim: 1. The process for, improving the stability to consisting of hydrogen and alkyl groups of 1 to 3 carbon atoms, and M is selected from the group consisting of alkali metals and the ammonium radical, said solution having a pH of at least '5 and less than 7.

2. The process for improving the stability to discoloration of a diazotype print, bearing residual unreacted coupling component and diazo compound decomposition products on the back-. ground areas thereof, which comprises the step of washing said print after its development with an aqueous solution of a neutral water-soluble inorganic salt and a compound having the gen-. "eral formula:

consisting of alkali metals and the ammonium radical, said solution having a pH of at least 5 and less than 7.

3. The process for improving the stability to discoloration of a diazotype print, bearing residual unreacted coupling component and diazo compound decomposition products on the back ground areas thereof, which comprises the step'. of washing said print after its development with.

an aqueous solution containing at least 1% of a compound having the general formula:

wherein R1 and R2 are selected from the group consisting of hydrogen and alkyl groups of l to 3 carbon atoms, and M is selected from the group consisting of alkali metals and the ammonium radical, said solution having a pH of at least 5 and less than 7.

4, The process for improving the stability to discoloration of a diazotype print, bearing resid---- ual unreacted coupling component and diazocompound decomposition products on the back-,

ground areas thereof, which comprises the step of washing said print after its development with an aqueous solution containing 5% by weight of;

a compound having the general formula:

Rz-O

R, o 1 =o wherein R1 and R2 are selected from the group consisting of hydrogen and alkyl groups of 1 to 3 carbon atoms, and M is selected from the group consisting of alkali metals and the ammonium radical, said solution having a pH of at least 5 and less than 7.

5. The process for improving the stability to discoloration of a' diazotype print, bearing reside ual unreacted coupling component and diazo compound decomposition products on the background areas thereof, which comprises the step of washing said print after its development with an aqueous solution of sodium dihydrogen phosphate.

6. The process for improving the stability to discoloration of a diazotype print, bearing residual unreacted coupling component and diazo compound decomposition products on the background areas thereof, which comprises the step of washing said print after its development with an aqueous solution containing sodium dihydrogen phosphate and sodium chloride.

7. The process for improving the stability to discoloration of a diazotype print, bearing residual unreacted coupling component and diazo REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,967,371 Schmidt et a1 July 24, 1934 15 2,113,944 Leuch Apr. 12, 1938 2,442,061 Slifkin May 25, 1948 

